Comparison of inter- and intraobserver agreement between three types of fetal volume measurement technique (XI VOCAL, VOCAL and multiplanar)

Objectives: To compare the new XI VOCAL (eXtended Imaging Virtual Organ Computer-aided Analysis) for three-dimensional (3D) ultrasound measurement of fetal volume with the conventional multiplanar technique and a rotational method using VOCAL.

Methods: We acquired 3D volume datasets from 30 fetuses at 11-14 weeks of gestation using a commercially available ultrasound system. Fetal volume was calculated using XI VOCAL (with 5, 10, 15 and 20 slices), multiplanar (1-mm interval) and VOCAL (with 12 degrees, 18 degrees and 30 degrees rotation) techniques. The level of agreement for interobserver and intraobserver variability was determined and evaluated for all methods and reliability was assessed.

Results: Fetal volume measurements obtained using XI VOCAL (10 slices) showed good correlation with those obtained using VOCAL (18 degrees) (r = 0.940, P = 0.076; intraclass correlation coefficient (ICC), 0.962 (95% CI, 0.920-0.982), P = 0.182), and XI VOCAL (15 slices) showed good correlation with VOCAL (12 degrees ) (r = 0.961, P = 0.092; ICC, 0.979 (95% CI, 0.957-0.990), P = 0.190). The mean difference between paired measurements by the XI VOCAL (10 slices) and VOCAL (18 degrees ) methods was 1.00 mL, while that by the XI VOCAL (15 slices) and VOCAL (12 degrees) methods was 0.90 mL. 95% limits of agreement were - 2.80 to 4.80 between XI VOCAL (10 slices) and VOCAL (18 degrees) and - 1.90 to 3.70 between XI VOCAL (15 slices) and VOCAL (12 degrees). There was a small difference in the time required to complete the fetal volume measurement between XI VOCAL and VOCAL when a similar number of slices or rotational steps was used (P < 0.05), XI VOCAL taking less time.

Conclusion: XI VOCAL (with 10, 15 and 20 slices) can be used interchangeably with the multiplanar technique (1-mm interval) for the measurement of fetal volume. XI VOCAL (10 slices) and VOCAL (18 degrees) can be used interchangeably, as can XI VOCAL (15 slices) and VOCAL (12 degrees), for the measurement of fetal volume.